Method for ablation of heart tissue

ABSTRACT

A dual curve ablation catheter (2), especially suited for treating atrial flutter, includes a shaft (4) with a deflectable tip (20) at the distal end (6) and a handle (10) at the proximal end (8). The tip includes a highly flexible distal segment (30), a relatively stiff intermediate segment (28) and a flexible proximal segment (26) so that pulling on a manipulator wire (16) attached to the distal segment causes the distal segment to curve and engage, for example, an isthmus of tissue (106) adjacent the tricuspid valve (104) and the inferior vena cava (98) and causes the proximal segment to curve and press against the wall (110) of the inferior vena cava so to stabilize the catheter. Ablation energy can be supplied through the ablation electrodes (48, 68) simultaneously or one at a time to ablate tissue at the isthmus without the need for moving the catheter.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 08/825,425, filed Mar. 28,1997, now U.S. Pat. No. 5,916,214, which is a continuation ofapplication Ser. No. 08/429,429, filed May 1, 1995, now abandoned, thedisclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

It has long been known that the action of the heart depends uponelectrical signals carried along the surface of the heart tissue.Sometimes these electrical signals become faulty. It has been found thatablating (burning) these cardiac conduction pathways in the region ofthe problem destroys the tissue to eliminate the faulty signal.Electrophysiology (EP) catheters are catheters having one or moreelectrodes at their tips and are used for both diagnosis and therapy.The electrodes at their tips of EP catheters allow the physician tomeasure electrical signals along the surface of the heart (calledmapping) and then, when necessary, ablate certain tissue using,typically, radio frequency (RF) energy directed to one or more highenergy capable ablation electrodes.

SUMMARY OF THE INVENTION

The present invention is directed to an EP ablation catheter especiallysuited for treating atrial flutter. Atrial flutter is a common rhythmdisturbance defined as an atrial tachycardia with atrial rates exceeding240 beats per minute. The invention creates a linear lesion orientedperpendicularly to the isthmus of tissue between the inferior aspect ofthe tricuspid valve and the inferior vena cava. The invention ablates aline of tissue across the critical isthmus using ablation-capableelectrodes positioned along the tip of the catheter. The catheter isdesigned to remain in place and provide firm electrode contact duringthe ablation despite respiratory, cardiac or blood motion during theablation.

The atrial flutter ablation catheter includes a shaft having proximaland distal ends with a deflectable tip at the distal end and a handle atthe proximal end. The tip includes a highly flexible distal segment, arelatively stiff intermediate segment and a flexible proximal segment.Pulling on a manipulator wire, passing through a lumen in the shaft andattached to the distal end the shaft, causes the distal and proximalsegments of the tip to curve. When properly positioned for treatingatrial flutter, the distal segment engages the isthmus of tissue to beablated, which lies adjacent the tricuspid valve and the inferior venacava opening into the right atrium, and the proximal curve segmentpresses against the wall of the inferior vena cava so to stabilize thecatheter. Ablation energy is supplied through the ablation electrodes,preferably one at a time, to ablate the tissue at the isthmus withoutthe need for moving the catheter once in position.

A rotatable core wire, passing the central lumen and secured to the tipof the shaft, may be used to permit a torquing force to be applied tothe distal end of the shaft without rotating the entire catheter. Thetemperature of the ablation electrodes is preferably monitored, such asusing thermocouple wires, to permit enhanced control over the ablationtemperatures.

One of the advantages of the invention is that it uses a series ofablation electrodes instead of one long electrode to ablate the cardiactissue. Making the ablation electrodes electrically isolated from oneanother and allowing them to be individually powered permits a lowerpower ablation energy source to be used than would be required if themultiple ablation electrodes were replaced by one long electrode or ifthe multiple ablation electrodes were all powered simultaneously. Also,multiple electrodes allows bipolar recording to be conducted. Of course,if a power source has sufficient capacity to power more than oneablation electrode, this can be done also.

Other features and advantages of the invention will appear from thefollowing description in which the preferred embodiment has beendiscussed in detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall view of an atrial flutter ablation catheter madeaccording to the invention;

FIG. 1A illustrates the tip of the catheter of FIG. 1 in which theproximal segment has a radius of curvature smaller than that of FIG. 1;

FIG. 2 is a simplified view showing placement of the tip of the catheterof FIG. 1 within the inferior vena cava, right atrium and against theisthmus adjacent the tricuspid valve;

FIGS. 3A and 3B are enlarged cross-sectional views of the tip of thecatheter of FIG. 1 omitting the electrical conductor and thermocouplewires passing through the central lumen of the body of the cathetershaft;

FIG. 3C is an enlarged side view of a segment of the catheter shaft ofFIG. 1;

FIGS. 3D-3F are cross-sectional views taken along lines 3D--3D through3F--3F in FIG. 3A;

FIGS. 3G and 3H are cross-sectional views taken along lines 3G--3G and3H--3H in FIG. 3B;

FIG. 3I is a cross-sectional view taken along line 3I--3I in FIG. 3C;

FIG. 4 is a side view showing the tapered nature of the core wire;

FIG. 5 shows a core wire of FIG. 4 with a hypotube, shown in FIG. 7, anda polyimide tube shown in FIG. 6, strategically positioned along thelength of the core wire to provide a very flexible distal segment, amoderately flexible proximal segment and a relatively stiff intermediatesegment for the deflectable tip of the catheter of FIG. 1;

FIGS. 6 and 7 are cross-sectional views of the polyimide tube andhypotube shown in FIG. 5;

FIG. 8 is an enlarged view of the distal segment of the tip of thecatheter of FIG. 1;

FIGS. 8A-8E are views similar to FIG. 8 of alternative embodiments ofthe distal segment of the tip of the catheter of FIG. 1;

FIG. 9 shows the distal portion of the assembly of FIG. 5 illustratingthe positions of the proximal and distal curves relative to thepositions of the various tubes mounted over the core wire; and

FIG. 10 is a schematic illustration showing the interconnections amongthe catheter of FIG. 1, a switchbox, an R.F. generator and anindifferent electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates an anatomically-conforming dual curve ablationcatheter, in particular an atrial flutter ablation catheter 2, includinga catheter shaft 4 having a distal end 6 and a proximal end 8. Proximalend 8 is mounted to a handle 10 having an axially slidable manipulatorring 12 and a rotatable lateral deflection ring 14 operably connected toa manipulator wire 16 and a core wire 18, respectively, shown in FIGS.3A and 3D. Sliding manipulator ring 12 causes a deflectable tip 20 ofcatheter shaft 4 to deflect as shown in FIGS. 1 and 2 while rotatingring 14 causes lateral deflection of tip 20 through the torquing actionof core wire 18.

Handle 10 also includes an electrical connector 21 connected toelectrical conductors 22, 23 and thermocouple wires 24, 25. Handle 10may be of a conventional design, or as shown in U.S. Pat. No. 5,318,525or in application Ser. No. 08/343,310 filed Nov. 22, 1994, thedisclosures of which are incorporated by reference.

Deflectable tip 20 includes three segments, a proximal segment 26, anintermediate segment 28 and a distal segment 30. The construction ofdistal segment 30 can be seen best with reference to FIGS. 1, 3A-3F, 4,5 and 9. Shaft 4 at tip 20 is seen to include a 5-lumen shaft body 32made of Pebax®, a polyamide polyether block copolymer made by ElfAtochem, Inc. of Philadelphia, Pa. To impart more flexibility to thissection, the Pebax® material is a relatively lower durometer material,such as 30-40 D. Body 32 includes a central lumen 34 and four satellitelumens 36 extending along the length of body 32. A part of central lumen34 is occupied by a tubular layer 38 made of polyimide tubing. Core wire18 fits loosely within central lumen 34 while electrical conductor 22and thermocouple wires 24 pass through two different satellite lumens36. The other electrical conductor 23 and thermocouple wires 25 passesthrough central lumen 34.

The portion of shaft 4 proximal of deflectable tip 20, see FIGS. 3C and3I, is relatively stiff to permit controlled placement of tip 20 at thetarget site as discussed below. Such proximal portion of the shaft 4includes an outer jacket 39, preferably made of higher durometer Pebax®,such as 55-65 D, reinforced by braided wires 41. A polyimide our ultemtubular layer 38a is positioned within the central lumen 34a and housescore wire 18, electrical connectors 22, 23, thermocouple wires 24,25 andmanipulator wire 16.

If desired, one or more axially slidable core wires could be used withthe distal ends of the core wires positionable at different axialpositions along tip 20; doing so would permit the size of the curves oftip 20 to be changed. FIG. 1A illustrates the result of using such aslidable core wire. Tip 20a has a curve at proximal segment 26 with alarger radius than that if FIG. 1; the curves at distal segments 30 arethe same for both figures. An example of a catheter with a variablecurve tip is described in U.S. patent application Ser. No. 08/343,310for Steerable Electrophysiology Catheter, the disclosure of which isincorporated by reference.

The distal end 42 of shaft body 32, see FIG. 3A, lies adjacent aninsulator 44 made of PEEK (poly-ether-ether-keytone) or other hard,temperature-resistant material. Insulator 44 is bonded to distal end 42of shaft body 32 by heat fusing and adhesive.

Insulator 44 has five bores or lumens which generally align with thecorresponding lumens formed in shaft body 32. A cylindrical ablationelectrode 48 is secured to and extends between insulator 44 and a secondinsulator 50. A tip electrode 68 is secured to the distal end ofinsulator 50. The connections between electrodes 48, 68 and insulators44, 50 are preferably through both a snap fit and the use of adhesivesor other bonding techniques. Tubular layer 38 terminates at a centralbore in insulator 50 and is affixed thereto by adhesive.

Manipulator wire 16 has a ball 70 at its distal end to preventmanipulator wire 16 from being pulled back through one of the bores 72formed in insulator 44. As seen in FIG. 3D, insulator 50 has four axialbores housing core wire 18, thermocouple wires 24, electrical conductor22 and the distal end 76 of core wire 18.

It should be noted that in FIGS. 3A and 3B electrical conductor 23 andthermocouple wires 25 are not shown. High power electrical conductors22, 23 are connected to ablation electrodes 48, 68 in conventionalmanners, such as soldering or welding. Pairs of thermocouple wires 24,25 are respectively positioned adjacent ablation electrodes 68, 48 so topermit the temperatures of the ablation electrodes to be monitored. Thehollow interior 78 of tip electrode 68 is filled with a thermallyconducting but electrically insulating material, such as cyanoacrylateadhesive, so that thermocouple wires 24 positioned within interior 78will be provided an accurate reading of the temperature of tip electrode68, without electrical continuity between the two. As shown in FIG. 3E,thermocouple wires 25 and conductor 22 are positioned adjacent electrode48 by elastically insulating materials 79, 81.

Of the proximal, intermediate and distal segments 26, 28, 30,intermediate segment is the stiffest and distal segment 30 is the leaststiff while proximal segment 26 has a stiffness somewhat between the twostiffnesses of segments 28, 30. To provide shaft 4 with these threedifferent stiffness for tip 20, core wire 18 is modified to providethese stiffnesses. Core wire 18 is, in one preferred embodiment, about60 inches (152 cm) long and has five distinct segments. Proximal segment80 is about 35-39 inches (89 to 99 cm) long and has a diameter of about0.025 inch (0.64 mm). A second segment 82 tapers in diameter from 0.025inch to 0.018 inch (0.46 mm) over a distance of about 3 inches (7.6 cm).Third segment 84 is a constant 0.018 inch diameter over a length ofabout 12-14 inches (30 to 36 cm). These first three segments 80, 82, 84are all coated with PTFE to minimize friction within shaft 4. The fourthsegment 86 core wire 18 tapers from 0.018 inch to 0.0085-0.0095 inch(0.46 mm to 0.22 to 0.24 mm) over a length of 1.5-2.5 inches (3.8 to 6.4cm) while the final 5-inch (13 cm) length of core wire 18 is a constantdiameter fifth segment 88, having a diameter of 0.0085-0.0095 inch.

FIGS. 3B, 3G and 5 illustrate how the different stiffnesses for segments26, 28 and 30 is achieved. A hypotube 90, made of stainless steel, isshown in cross-section in FIG. 7. Hypotube 90 has an inside diameter of0.010-0.012 inch (0.25 to 0.30 mm) and an outside diameter of0.018-0.022 inch (0.46 to 0.56 mm) and is used to cover core wire 18over intermediate segment 28. Hypotube 90 extends for a distance ofabout 1.0-2.0 inch (2.5-5 cm) in a proximal direction along core wire 18to ensure that the portion of tip 20 between sections 26 and 30 isrelatively stiff. Polyimide tube 92 with an inside diameter of0.0185-0.0225 inch (0.47 to 0.57 mm) and an outside diameter of0.024-0.028 inch (0.61 to 0.71 mm) and a length of 0.25-0.5 inch(6.35-12.7 mm) is mounted over hypotube 90 within segment 30. A secondpolyimide tube 93 with the same I.D. and O.D. as polyimide tube 92 and alength of 1.0-1.5 inch (2.5-3.8 cm) fits over the extension of hypotube90 within segment 26. In the preferred embodiment, distal segment 30 isabout 1.0-2.0 inches (2.54-5.08 cm) long, intermediate segment 28 isabout 1.4-2.2 inch (3.5 to 5.5 cm) long and proximal segment 26 is about0.8-1.6 inches (2.0-4.0 cm) long. Note that hypotube 90 and polyimidetubes 92, 93 are shown only in FIGS. 3B, 3G and 5-7 for simplicity ofillustration. The maximum angle for the primary curve at proximalsegment 26 is about 120° and for the secondary curve at distal segment30 is about 100°.

FIG. 9 illustrates how the core wire design matches with the curveshape. In addition to a core wire assembly with sections havingdifferent stiffnesses, shaft 4 and intermediate and distal segments 28and 30 are made having different duometer hardnesses of about 65 D, 55 Dand about 30-40 D, respectively.

The use of catheter 2 will be described in conjunction with FIG. 2. FIG.2 illustrates, in simplified form, a portion of a heart 94 having asuperior vena cava 96 and an inferior vena cava 98 opening into a rightatrium 100. Also illustrated is a portion of right ventricle 102separated from right atrium 100 by a tricuspid valve 104. An isthmus oftissue 106 extends between the inferior aspect of tricuspid valve 104and inferior vena cava 98 adjacent the opening of the coronary sinus108. Distal segment 30 is sized with an appropriate flexibility so thatupon pulling of manipulator wire 16, distal segment 30 assumes thecontour generally corresponding to the shape of the coronary tissue atisthmus 106 when oriented perpendicular to the isthmus of tissue 106.Intermediate segment 28 is sufficiently stiff, through the use of bothhypotube 90 and polyimide tube 92, so that it remains substantiallystraight when distal segment 30 is properly flexed. Proximal segment 26is less stiff than intermediate segment 28 but, in the preferredembodiment, stiffer than distal segment 30 but also has a curve whichallows proximal segment 26 of shaft 4 to push against or be bracedagainst the wall 110 of inferior vena cava 98. This stabilizes tip 20 ofcatheter 2 to help maintain distal segment 30 in the proper position atisthmus of tissue 106.

After any appropriate readings are taken, ablation electrodes 48, 68 arepositioned along isthmus of tissue 106. Once in position, electrodes 48,68 can be coupled to a suitable RF power supply, not shown, throughconnector 21. One such power supply is shown in U.S. patent applicationSer. No. 08/179,558, filed Jan. 10, 1994, the disclosure of which isincorporated by reference. Ablation electrodes 48, 68 are electricallyisolated from one another so they can be independently powered from thepower supply. This means that the power supply need not be as large aswould be required if they were electrically connected to one another orif the separate ablation electrodes were replaced by a single,extra-long ablation electrode. This eliminates the need to move theablation electrode after each application of power, the "burn-drag-burn"technique used with conventional ablation catheters. Ablation electrodes48, 68 are powered one-at-a-time.

Typically, a switchbox 130 is connected between the ablation catheter 2and an RF generator 132. See FIG. 10. Switchbox 130, which can also beconnected to an indifferent electrode 134, allows RF current to bedirected to any available ablation electrodes. Thermocouple signals fromthe particular electrode, used for temperature control, are alsosupplied to switchbox 130. More than one ablation electrode andthermocouple can be connected simultaneously using switchbox 130.Switchbox 130 can also be automatically controlled.

FIGS. 8-8E illustrate various configurations of ablation-capable andmapping electrodes which can be used. FIG. 8 shows ablation-capableelectrodes 48, 68, each 4 mm long and having an outside diameter of0.091 inch (2.3 mm), for catheter 2 of FIGS. 1-7. Distal segment 30a ofthe embodiment of FIG. 8A is like distal segment 30 of FIG. 8 but hastwo mapping band electrodes 120. FIG. 8B shows a distal segment 30b withtwo ablation-capable band electrodes 48 and a half-size (2 mm long)mapping tip electrode 122. Distal segment 30c of FIG. 8C adds two bandmapping electrodes 120 to the embodiment of FIG. 8B. The embodiment ofFIG. 8D shows the use of a spiral-wound or coiled ablation-capableelectrode 124 adjacent to a mapping tip electrode while the FIG. 8Eembodiment adds a pair of mapping band electrodes 120 to the FIG. 8Dembodiment. Other electrode arrangements are also possible.

Modification and variation can be made to the disclosed embodimentwithout departing from the subject of the invention as defined in thefollowing claims. For example, materials, diameters and lengths can bechanged to suit the particular needs or desires of the user. Theattachment and bonding techniques discussed above are merely exemplary;other chemical, mechanical and/or thermal bonding techniques can be usedas well. In some cases it may be desired to apply energy to more thanone ablation electrode at the same time; for example, four ablationelectrodes could be used and powered two-at-a-time. The portion ofdistal segment 30 carrying ablation-capable electrodes 48 could be madeto be curved or curvable if desired. While the invention has itsgreatest utility as an atrial flutter ablation catheter, it may alsofind use in ablating tissue at the mitral valve, in addition totricuspid valve 104, and accessory pathways in the postero-lateral rightventricle. Other curve sizes and spacings for this dual curve cathetercould also make it suitable for mapping and ablating other areas of theheart.

What is claimed is:
 1. A method for ablation of heart tissue at a targetsite comprising the following steps:passing a distal segment of anablation catheter into a chamber of a heart; manipulating the distalsegment of the ablation catheter to the target site; curving said distalsegment as necessary to generally conform to any curvature of the targetsite; placing the curved distal segment against the target site; bracinga second segment of the ablation catheter near the target site; applyingablation energy to an ablation electrode at the distal segment to ablateheart tissue at the target site; and maintaining at least a portion ofsaid distal segment substantially in position against the target siteduring the ablation energy applying step.
 2. The method according toclaim 1 wherein the target site is an isthmus of tissue adjacent atricuspid valve in an inferior vena cava.
 3. The method according toclaim 1 wherein the ablation energy applying step is carried out bysequentially applying ablation energy to a plurality of electricallyisolated ablation electrodes spaced apart along at least the distalsegment to ablate heart tissue at an isthmus of tissue.
 4. The methodaccording to claim 1 wherein the ablation energy applying step iscarried out by simultaneously applying ablation energy to at least twoablation electrodes.
 5. The method according to claim 1 wherein themanipulating step includes the steps of selectively applying a torquingforce to said distal segment thereby causing said distal segment, whencurved, to move laterally.
 6. The method according to claim 1 whereinthe curving step is carried out by pulling on a manipulator wireconnected to said distal segment and passing through a lumen in theablation catheter.
 7. The method according to claim 1 wherein bracing asecond segment of the ablation catheter includes bracing the secondsegment against a wall of an inferior vena cava.
 8. The method accordingto claim 7 wherein the bracing step is carried out by pulling on amanipulator wire passing through a lumen in the ablation catheter. 9.The method according to claim 7 wherein the curving and bracing stepsare carried out by pulling on a manipulator wire passing through a lumenin the ablation catheter.
 10. The method according to claim 7 furthercomprising the step of providing a tubular ablation catheter shafthaving an intermediate segment between the distal and second segmentsand an axially movable manipulator wire extending through a lumen in thetubular ablation catheter shaft and secured to said distal segment, theintermediate segment being substantially stiffer than the second segmentand the second segment being at least as stiff as the distal segment,the curving step being carried out by pulling on the manipulator wirethereby curving the distal and second segments while the intermediatesegment remains substantially straight.
 11. The method according toclaim 1 further comprising the step of monitoring a temperature of saidablation electrode.
 12. The method according to claim 1 furthercomprising the step of electrically mapping an area of the heart at ornear an isthmus of tissue.
 13. The method according to claim 12 whereinthe mapping step is carried out using at least one mapping electrodemounted to the ablation catheter proximal of said ablation electrode.14. The method according to claim 13 wherein the mapping step is carriedout using at least one mapping electrode distal of said ablationelectrode.
 15. The method according to claim 1 wherein bracing thesecond segment includes positioning the second segment against tissueproximate the target site.
 16. The method according to claim 1 furthercomprising the step of completing ablation of the target site.
 17. Themethod according to claim 16 wherein the target site is an isthmus oftissue.
 18. The method according to claim 16 wherein completing targetsite ablation includes ablating a plurality of tissue locations.
 19. Themethod according to claim 18 wherein the step of ablating a plurality oftissue locations occurs without movement of the distal segment.
 20. Amethod for treating atrial flutter through ablation of heart tissuecomprising the following steps:passing a distal segment of an ablationcatheter through an inferior vena cava and into a right atrium of aheart; manipulating the distal segment of the ablation catheter to anisthmus of tissue adjacent a tricuspid valve and the inferior vena cava;curving said distal segment to generally conform to the curvature of theisthmus of tissue; placing the curved distal segment against the isthmusof tissue; bracing a second segment of the ablation catheter against awall of the inferior vena cava; applying ablation energy to an ablationelectrode at the distal segment to ablate heart tissue at the isthmus oftissue; and maintaining at least a portion of said distal segmentsubstantially in position against the isthmus of tissue during theablation energy applying step.
 21. A method for treating atrial flutterthrough ablation of heart tissue comprising the following steps:passinga distal segment of an ablation catheter through an inferior vena cavaand into a right atrium of a heart; manipulating the distal segment ofthe ablation catheter to an isthmus of tissue adjacent a tricuspid valveand the inferior vena cava; electrically mapping an area of the heart ator near the isthmus of tissue using at least one mapping electrodemounted to the ablation catheter; curving said distal segment togenerally conform to the curvature of the isthmus of tissue; placing thecurved distal segment against the isthmus of tissue; bracing a secondsegment of the ablation catheter against a wall of the inferior venacava; sequentially applying ablation energy to electrically isolatedablation electrodes spaced apart along at least the distal segment toablate heart tissue at the isthmus of tissue; monitoring the temperatureof at least one of said ablation electrodes; and maintaining at least aportion of said distal segment substantially in position against theisthmus of tissue during the ablation energy applying step.
 22. A methodfor the ablation of heart tissue at a target site comprising thefollowing steps:passing a distal segment of a catheter having aplurality of ablation electrodes on the distal segment into the rightatrium of a heart; manipulating the distal segment of the catheter to anisthmus of tissue between an inferior aspect of a tricuspid valve and aninferior vena cava; curving the distal segment to generally conform tothe curvature of the isthmus of tissue; placing the curved distalsegment against the isthmus of tissue; and applying ablation energy tothe plurality of electrodes such that the isthmus of tissue is ablatedwithout moving the curved distal segment.
 23. The method according toclaim 22 wherein ablation energy is applied by sequentially applyingablation energy to the plurality of ablation electrodes.
 24. The methodaccording to claim 22 wherein ablation energy is applied simultaneouslyto at least two ablation electrodes.
 25. The method according to claim22 wherein the ablation energy applied to ablate the isthmus of tissueis sufficient to treat atrial flutter in the patient.